Known image forming apparatuses, such as laser printers, generally include an attachable/detachable process cartridge that includes a photosensitive drum for carrying a toner image, which is formed by developing an electrostatic latent image on the photosensitive drum. The toner image carried on the photosensitive drum is generally transferred onto a sheet that is fed between the photosensitive drum and a transfer roller. The transfer roller is disposed so as to confront the photosensitive drum.
In some image forming apparatuses, such as the image forming apparatus disclosed in Japanese Laid-Open Patent Publication No. 2000-267547, a transfer roller is provided in a process cartridge. Process cartridges including transfer rollers are generally larger in size. An image forming apparatus that is capable of accommodating such a process cartridge generally needs to allocate a larger space for installing/removing the larger-sized process cartridge into/from the image forming apparatus. Thus, the overall size of such an image forming apparatus must also be larger.
To avoid such problems, in some image forming apparatuses, a transfer roller is provided on a frame of the image forming apparatus rather than on a process cartridge. Because the transfer roller is provided on the frame of the image forming apparatus, a smaller process cartridge can be produced. As a result, the amount of space allocated in the image forming apparatus for installing and removing the process cartridge may be reduced and the overall size of the image forming apparatus may also be reduced.
When a transfer roller is provided on a frame of an image forming apparatus rather than on a process cartridge, a portion of the photosensitive drum that faces the transfer roller will be exposed when the process cartridge is detached/removed from the image forming apparatus. Such exposure of the photosensitive drum can result in damage to the photosensitive drum.
To reduce the possibility of such damage to a photosensitive drum, an openable/closeable shutter for covering the exposed part of the photosensitive drum can be provided on the process cartridge. When the process cartridge is removed from the image forming apparatus, the shutter is closed to cover the part of the photosensitive drum that would otherwise be exposed. When the process cartridge is set in the image forming apparatus, the shutter is opened to expose part of the photosensitive drum.
Providing such a shutter, however, increases the number of components needed to manufacture a process cartridge, and causes complex structures to be included on the process cartridge. As a result, the cost of manufacturing the process cartridge, and, in turn, the image forming apparatus capable of accommodating such a process cartridge increases.